This application claims the priority of Japanese Patent Application No. 11-212373 filed on Jul. 27, 1999, and Japanese Patent Application Nos. 2000-89742, 2000-89743, 2000-89744 and 2000-89745 filed on Mar. 28, 2000, which are incorporated herein by reference.
This invention is related to a microcapsule and, in particular, to improvement in stability, feel of use, releasing characteristics of the encapsulated oil droplets and dispersibility of the microcapsule.
Microcapsules having oil droplets encapsulated within a capsule have been studied in such fields as foods, medicines, cosmetics, and the like. For example, there have been attempts to improve the stability of a drug in a product by compounding a microcapsule having the drug encapsulated therein.
Known as a method of making a microcapsule is one comprising the steps of: preparing an O/W emulsion from an oil phase to become an encapsulated oil droplet and a water phase containing a capsulating agent; shaping this emulsion into a fine particle; and forming a capsule. Its examples include: a method in which the O/W emulsion is further dispersed and emulsified into an outer oil phase so as to form an O/W/O emulsion, and its water phase is hardened so as to form a capsule; a spray-cooling method in which the O/W emulsion is hardened while being sprayed in air; a dripping method in which the O/W emulsion is dripped from a nozzle so as to be hardened in a gas or liquid; and the like.
In conventional emulsifying methods, however, it is difficult for the O/W emulsion to have an emulsified particle size of 1 xcexcm or less. Even if an O/W emulsion having an emulsified particle size of 1 xcexcm or less can be made, the stability of such emulsion is insufficient, whereby oil droplets tend to fuse together, thus increasing the size of oil droplets encapsulated within the microcapsule. In such a case, there has been a problem that the microcapsule diameter is required to increase in order to enhance the capsulating efficiency of encapsulated oil droplets.
In the method via an O/W/O emulsion in particular, the O/W emulsion is further dispersed and emulsified into the outer oil phase, whereby not only the fusion between the encapsulated oil droplets but also the unification between the encapsulated oil droplets and the outer oil phase is likely to occur. Therefore, it has been problematic in that temperature and stirring speed are restricted upon the O/W/O emulsification, the particle size of microcapsule is very hard to control, and the stability of resulting microcapsule is not sufficient. Also, it has been desired to suppress loss in the inner oil phase at the time of making.
Further, the stability of microcapsule when compounded with other base materials, its feel of use on skin, and releasing characteristics of encapsulated oil droplets are important. For example, a microcapsule is likely to be destroyed when added in a making step of products such as milky lotion and cream, which are obtained as being stirred at a high speed in a viscous medium. It has conventionally been very difficult to obtain a microcapsule which would not be destroyed in the step of making such products. Also, as for releasing characteristics of encapsulated oil droplets when applied as being spread on skin, microcapsules having respective releasing characteristics such as:
(1) immediately-releasing microcapsules which are destroyed without a sense of incompatibility and release encapsulated oil droplets therefrom rapidly;
(2) gradually-releasing microcapsules which release encapsulated oil droplets therefrom gradually; and
(3) non-releasing microcapsules which maintain encapsulated oil droplets and does not release them therefrom
are desired depending on various purposes.
Japanese Unexamined Patent Publication No. 9-255562 reports an O/W/O emulsion in which a hydrophilic polymer and an organophilic clay mineral are compounded with its water phase and outer oil phase, respectively. However, there have been cases where, when an O/W particle is taken out from this O/W/O emulsion or the O/W/O emulsion per se is compounded with other base materials so as to form a product, the capsule is destroyed due to mechanical shearing or changes in base compositions in the step of making the product. Also, taking out an O/W particle from this O/W/O emulsion has been problematic in that contraction or destruction occurs, and that its dispersibility is unfavorable when dispersed in base materials again.
In view of the above-mentioned problems of the prior art, it is an object of the present invention to provide a microcapsule which is not destroyed even when compounded with other base materials so as to form a product, and exhibits favorable storage stability and feel of use, whose encapsulated oil droplets are (1) released immediately, (2) released gradually, or (3) not released at all when applied on skin.
It is another object of the present invention to provide a microcapsule which does not contract in air and exhibits a favorable dispersibility to various medium, whereas the elution of its encapsulated components is low in the medium.
Still another object of the present invention is to provide a method of making a microcapsule which can make such a microcapsule easily and efficiently, and also can easily control the microcapsule particle size over a wide range.
As the result that the inventors have carried out studies in view of the above-mentioned problems of the prior art, it has been found that, if a hydrophilic polymer gelling agent, one which hardens by heating and cooling in particular, is used as a main gelling agent, a microcapsule which is not destroyed even when compounded with other base materials so as to form a product and has a favorable storage stability can be obtained. Also, it has been found that, if the fracture strength of the microcapsule is within a specific range, releasing characteristics of encapsulated oil droplets can be controlled over a range from immediately-releasing to non-releasing.
Further, it has been found that when the microcapsule based on a hydrophilic polymer gelling agent is coated, the contraction in air, dispersibility to various medium, and elusion of encapsulated components in medium can be also improved, thereby accomplishing the present invention.
Namely, a microcapsule in accordance with the present invention is one wherein an oil droplet having an average particle size of 0.01 to 3 xcexcm is encapsulated and a capsulating agent is a hydrophilic polymer gelling agent.
In the present invention, it is preferable that a fracture strength of the microcapsule is at least 10 g/cm2 but less than 500 g/cm2. Such a microcapsule can release the encapsulated oil droplet therefrom immediately when applied on skin.
Also, in the present invention, it is preferable that a fracture strength of the microcapsule is at least 500 g/cm2 but less than 2,000 g/m2. Such a microcapsule can release the encapsulated oil droplet therefrom gradually when applied on skin.
Also, in the present invention, it is preferable that a fracture strength of the microcapsule is at least 2,000 g/cm2 but 5,000 g/cm2 or less. Such a microcapsule does not release the encapsulated oil droplet therefrom when applied on skin.
In the present invention, it is preferable that the capsulating agent comprises essentially a hydrophilic polymer gelling agent which hardens by heating and cooling.
Preferred hydrophilic polymer gelling agent is agar or carrageenan.
Also, in the present invention, it is preferable that the microcapsule comprises a hydrophilic nonionic surfactant and a water-soluble solvent.
A microcapsule oily dispersion in accordance with the present invention is one wherein said microcapsule is dispersed in an oil phase.
The microcapsule oily dispersion is preferably obtained by the steps of:
preparing an O/W emulsion from an inner oil phase and a water phase containing the hydrophilic polymer gelling agent;
preparing an O/W/O emulsion by dispersing and emulsifying the O/W emulsion into an outer oil phase; and hardening the water phase of the O/W/O emulsion.
Also, the O/W emulsion is preferably prepared by the steps of:
preparing an oil-in-water-soluble-solvent type emulsion by adding the inner oil phase to a water-soluble solvent containing a hydrophilic nonionic surfactant; and
adding an aqueous solution of the hydrophilic polymer gelling agent to the oil-in-water-soluble-solvent type emulsion.
In the present invention, the microcapsule obtained by eliminating the outer oil phase of said microcapsule oil dispersion is preferable.
In the present invention, it is preferable that the microcapsule comprises an oil-soluble drug therein.
Also, in the present invention, it is preferable that the microcapsule comprises an organic UV-absorbing agent therein.
A cosmetic preparation in accordance with the present invention comprises said microcapsule.
A solid cosmetic preparation in accordance with the present invention comprises said microcapsule.
A sunscreen cosmetic preparation in accordance with the present invention comprises said microcapsule comprising an organic UV-absorbing agent therein.
A coated microcapsule in accordance with the present invention is one wherein said microcapsule coated with a coating agent.
In the present invention, it is preferably that the coating agent is a lipophilic or amphiphilic coating agent and, more preferably, a hydrophobic polysaccbaride.
Also, in the present invention, it is preferably that the coating agent is a hydrophilic coating agent.
A cosmetic preparation in accordance with the present invention comprises said coated microcapsule.
A method of making a microcapsule in accordance with the present invention comprises the steps of:
preparing an O/W emulsion from an inner oil phase and a water phase in which a hydrophilic polymer gelling agent hardening by heating and cooling has been dissolved with heating beforehand, at a hardening temperature of the gelling agent or higher, said O/W emulsion having an average particle size of 0.01 to 3 xcexcm;
preparing an O/W/O emulsion by dispersing and emulsifying the O/W emulsion into an outer oil phase at the hardening temperature of the gelling agent or higher; and
hardening and capsulating the water phase by cooling the O/W/O emulsion to the hardening temperature of the gelling agent or lower.
In the method of the present invention, it is preferable that the step of preparing the O/W emulsion comprises the steps of:
preparing an oil-in-water-soluble-solvent type emulsion by adding the inner oil phase into a water-soluble solvent containing a hydrophilic nonionic surfactant; and
mixing, at the hardening temperature of the gelling agent or higher, the oil-in-water-soluble-solvent type emulsion with an aqueous solution in which the hydrophilic polymer gelling agent hardening by heating and cooling has been dissolved with heating beforehand.
In the method of present invention, it is preferable that a gel prepared from the water phase has a fracture strength of at least 10 g/cm2 but less than 500 g/cm2.
Also, in the method of present invention, it is preferable that a gel prepared from the water phase has a fracture strength of at least 500 g/cm2 but less than 2,000 g/cm2.
Also, in the method of present invention, it is preferable that a gel prepared from the water phase has a fracture strength of at least 2,000 g/cm2 but 5,000 g/cm2 or less.